A motor nerve conduction block is defined as a reduction of either amplitude or area of the compound motor action potential elicited by proximal vs. distal motor nerve stimulation. The pathophysiological mechanisms leading to a figure of conduction block include segmental demyelination, recent axonal interruption, or various axonal excitability abnormalities due to ion channel dysfunction or membrane potential changes. These processes can be related to compressive, ischemic or dysimmune inflammatory causes. The etiologic diagnosis is established on the combination of clinical, electrophysiological, and biological data. Among the neuropathies that feature nerve conduction blocks, there is a group of particular dysimmune multifocal neuropathies characterized by long-term persistent conduction blocks, including pure motor forms and sensori-motor forms. The clinical, electrophysiological, biological, and therapeutic specificities of these two types of neuropathy will be discussed.